Common thin-film transistor (TFT) LCD varieties, including twisted nematic (TN), in-plane switching (IPS) and patterned vertical alignment (PVA), have a relatively slow intermediate gray scale response (e.g., as a pixel transitions from one gray level, or GL, to another) due to fundamental characteristics of the LCD structure constituting the pixels of the display. This slow response gives rise to poor dynamic contrast for motion video, resulting in display artifacts commonly known as “ghosting,” “blurring” and “streaking.” The best current solution to slow LCD response is response time compensation (RTC), often called “overdrive.” Overdrive compensates for slow intermediate gray scale response (so-called gray-to-gray, or GtG, transitions) by adjusting the gray scale values used to drive the LCD to achieve desired final values.
For example, it is not possible with current LCDs to drive a pixel from GL 20 to GL 180 in 8 ms. However, by initially driving the pixel from GL 20 toward GL 200 and then to GL 180 after a short delay, it is possible to achieve such a GtG transition in 8 ms.
LCDs typically use FROM-TO lookup tables (LUTs) to implement overdrive. A FROM-TO LUT takes the form of an N×N table that indicates the GL to which a pixel should be driven when going from one GL to another GL. However, a FROM-TO LUT that includes entries for every possible FROM and TO GL (e.g., 0 to 255) would be needlessly large. Instead, a typical FROM-TO LUT may be 17×17 and contain FROM-TO entries for 0 and 255 and multiples of 16 between the two, i.e. 0, 16, 32, . . . , 255. Interpolation is required for the remaining FROM and TO GLs that are not entered in the LUT. Bi-linear interpolation is used for this purpose and requires the four LUT entries corresponding to the closest GLs both less than or equal to and greater than both the FROM and TO GL.